The present invention relates to developer storage and dispensing apparatus. More specifically, the present invention is directed to developer dispensing apparatus for a developer station in an automatic electrostatographic printing machine.
Generally, in the process of electrostatographic printing, a photoconductive insulating member is charged to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive insulating layer is thereafter exposed to a light image of an original document to reproduced. This records an electrostatic latent image on the photoconductive member corresponding to the information areas contained within the original document. Alternatively, in a printing application, the electrostatic latent image may be created electronically by exposure of the charged photoconductive layer by an electronically controlled laser beam. After recording the electrostatic latent image on the photoconductive member, the latent image is developed by bringing a developer material charged of opposite polarity into contact therewith. In such processes the developer material may comrprise a mixture of carrier particles and toner particles or toner particles alone. Toner particles are attracted to the electrostatic latent image to form a toner powder image which is subsequently transferred to copy sheet and thereafter permanently affixed to copy sheet by fusing.
In such automatic printing machines, the toner material is consumed in a development process and must be periodically replaced within the development system in order to sustain continuous operation of the machine. Various techniques have been used in the past to replenish the toner supply. Initially, new toner material was added directly from supply bottles or containers by pouring to the dispensing apparatus fixed in the body of the automatic reproducing machine. The addition of such gross amounts of toner material altered the triboelectric relationship between the toner and the carrier in the developer resulting in reduced charging efficiency of the individual toner particles and accordingly a reduction of the development efficiency when developing the electrostatographic latent image on the image bearing surface. In addition, the pouring process was both wasteful and dirty in that some of the toner particles became airborne and would tend to migrate into the surrounding area and other parts of the machine. Accordingly, separate toner or developer hoppers with a dispensing mechanism for adding the toner from the hopper to the developer apparatus in the automatic printing machines on a regular or as needed basis have been provided. In addition, it has become common practice to provide replenishing toner supplies in a sealed container which when placed in the automatic printing machine can be automatically opened to dispense toner. In such systems as necessary the developer may be dispensed from the container relatively uniformly. Further difficulty may arise in uniformly dispensing the developer in that with a large mass of toner particles, which frequently are somewhat tacky, the particles may tend to agglomerate, become compacted and form a bridging structure in the toner container. In addition, with the use of removable or replaceable developer cartridges and due to the relative high cost of the developer contained therein, it is desirable to remove as much of the developer as possible during the dispensing operation from the cartridge so that only a minimal quantity of developer is not consumed in the dispensing operation and subsequently utilized in the formation of images. Excessive quantities of developer undispensed and remaining in a empty developer cartridge will increase the cost per copy to the consumer.
Various devices have been used to overcome the above-noted problems. For example, in the Xerox 1025 and 1038, the toner hopper is provided with a coiled spring auger which moves the toner material from one end of the hopper to the other. In the Xerox 1060, a similar wire or spring auger is provided in a toner bottle which is replaceable within the machine. In the systems, the augers are driven about one end and unsupported at the other end. Difficulties may be experienced in moving the maximum amount of toner from the bottle when the auger is trying to drive the toner away from the end of the auger which it is driven to the other end of the supply bottle to a dispensing opening resulting in excessive amounts of toner remaining in the bottle. Alternatively, if the auger is rotated in such a fashion as to transport the toner toward the drive end of the auger substantial quantities of toner can remain in the opposite end of the bottle because of the relatively low toner moving capacity of the unsupported end of the auger. In addition, in such a system in which a toner bottle has an auger to transport toner therein which is driven and supported about one end and intended to dispesne toner through a dispensing opening at the other end, as the auger is rotatbly driven tending to drive toner toward the dispensing end the amount of toner at the dispensing increases and tends to become compacted forming a bridge which tends to provide a force on the spring auger compressing it in a direction toward the driven end. If this force becomes to great, it may force the auger spring end past the dispensing opening in the toner cartridge thereby removing the antibridging function of the auger at the dispensing opening and resulting bridging over the dispensing opening and a lack of flow of toner out of the toner cartridge. This is a result of the auger being compressed toward its driven end so that the amount of opening in the dispensing opening is reduced resulting in smaller quantities of toner being dispensed on a continuing basis.